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  Weird F/A crank
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   Author  Topic: Weird F/A crank  (Read 380 times)
Nico
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Weird F/A crank
« on: September 28, 2018, 04:04:22 AM »
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I just took apart this 74 436 engine (case stamped 73) and found a crank that I've never seen before.
There's no labyrinth seal between the crankcases, instead there's this lump of steel. The inner crank webs each have half a pin that is pressed into this steel part. I was kind of expecting one of the webs to have a full pin that is pressed into the other web.
Is this normal for a 74 crank? The parts and shop manuals seem to show a regular labyrinth seal.
And anything in particular I need to know before rebuilding it?

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Bones
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Re:Weird F/A crank
« Reply #1 on: September 28, 2018, 09:16:19 PM »
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Lots of the F/A cranks like that one Nico. Seems to me maybe they went to that style part wat through 74 ? and through 75.
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Nico
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Re:Weird F/A crank
« Reply #2 on: September 30, 2018, 09:02:33 AM »
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Thanks Bones! That's good to know. I managed to get it apart, wasn't expecting it to be tapered! Took 14 tons to get it to let go.
What's the proper way to put it back together? I can't find anything about it in the shop manuals.
I'm thinking heat up the center, press the parts into each other both sides at once with a bunch of pressure, and let it cool down while keeping pressure on it.
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Green and Gold
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Re:Weird F/A crank
« Reply #3 on: October 1, 2018, 07:49:08 AM »
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I’d be interested in a few pics of your jig/pressing fixture/set up, if you have the time.
   
No first h and knowledge, but been told the trick of pressing them back together is keeping the two stub crank ends exactly 180 degrees apart; guys that do it for a living tell me its via experience……….  Good luck.
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Nico
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Re:Weird F/A crank
« Reply #4 on: October 1, 2018, 06:18:58 PM »
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Quote from: Green and Gold on October  1, 2018, 07:49:08 AM   

I’d be interested in a few pics of your jig/pressing fixture/set up, if you have the time.
   
No first h and knowledge, but been told the trick of pressing them back together is keeping the two stub crank ends exactly 180 degrees apart; guys that do it for a living tell me its via experience……….  Good luck.


I'll post some pictures tomorrow. Basically I turned my press into a puller to pull the crank apart from the center.
This one I think requires some more precautions than "normal" cranks as the pins towards the center are tapered. Can't just press it in and be done with it, gotta keep an eye on the length. The taper seems to be 1:50 so if you press a little too hard or too little the width can easily be off by a mm. The way it was it seemed to have around 0.09 mm of an interference fit around the taper, it was on there good!
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Nico
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Re:Weird F/A crank
« Reply #5 on: October 2, 2018, 06:58:06 AM »
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Ok, some pics..

First you need to get the bearings off. I made my own bearing puller, works pretty much the same as the factory puller. The reason for the top part being split too will become clear later.



Next I pressed the rod pins out on both sides.


That left me with the center webs being stuck to each other. You have to pull them apart. Here's my setup.

First bottom split plate.


Second bottom split plate, this is what you're going to be pressing on. Note that it is rotated 90 degrees compared to the first plate.


And the top plate, the top web is resting on this plate.


Some rods to reach down to the bottom plates. I threaded them on both ends to be able to fasten them just so they don't go flying. They don't really need to be this long.


The setup in the press looks something like this.



Now you can press on the bottom web down while keeping the top one in place, effectively pulling them apart. Now I didn't know that the center lump of steel was tapered and when it came off I had steel flying all over my shop, it came off hard! As it's tapered it lets go instantly and without warning, it's pretty much a cannon when it lets go. Make sure you keep a safe distance and put some padding underneath your press, I just use a box filled with bubblewrap and other soft stuff to catch the things that come flying down.

Now you're left with 2 seperate webs and the center lump attached to one of them. Here's where the bearing puller comes in again, it doubles as a puller plate for the center part. There's a 6 mm wide groove in it and that's what I use to hold onto it.


The hole in the center part of the crank goes all the way through so you can just press from the opposite side of it, no other magic involved.
The rest is easy, pull the center bearings, press the pins out.

Here's the crank in parts, the center tapered bits covered by tape as to avoid damaging them while pressing out the pins.
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T'nT 775 -71
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Blizzard 797 -71
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Green and Gold
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Re:Weird F/A crank
« Reply #6 on: October 3, 2018, 11:40:45 AM »
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Great pics, thanks for taking the time to post them.  I always wanted to try my hand at splitting a crank but knew I needed more dedicated fixtures.    Tried to press out a big end rod pin once and wound up launching things into a nearby wall.
     
Did you make your puller halves on a rotary table or cnc the stuff?  ½ in plate?
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Nico
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Re:Weird F/A crank
« Reply #7 on: October 3, 2018, 12:48:41 PM »
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Quote from: Green and Gold on October  3, 2018, 11:40:45 AM   

Great pics, thanks for taking the time to post them.  I always wanted to try my hand at splitting a crank but knew I needed more dedicated fixtures.    Tried to press out a big end rod pin once and wound up launching things into a nearby wall.
     
Did you make your puller halves on a rotary table or cnc the stuff?  ½ in plate?


The bearing puller I turned from 90 mm round stock in a regular hand operated lathe and then sawed the parts in half after putting the holes in. They're about 3/4 thick. I used 90 mm because that was the largest round stock I had laying around and I had a piece of 90mm ID hydraulic pipe that I could use for a retaining ring around it. If I had had a 100mm bar I'd have used that so it'd fit larger bearings too.
The press plates were 75-ish mm (or 3'' if you wish) wide flat bar that I cut to length and then just clamped 2 together in my milling vise and then used a hole saw and drilled/sawed on the border to put half a hole in each. They're 3/4 inch thick. The round one is a Volvo wheel spacer that happened to have the correct ID and OD
« Last Edit: October 3, 2018, 01:01:58 PM by Nico » Report to moderator Logged

R8 Euro -64
R10 Euro -65
Oly 494 -68
Alpine 370 -68
Oly 370 -69
Oly 277 mod -69
T'nT 292 -70
T'nT 292 -71
T'nT 640 -71
T'nT 775 -71
Elan 776 mod -71
Blizzard 797 -71
Mach Z 780 -96
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